Emily Dickinson Lexicon

NEC'ES-SA-RY, a. [L. necessarius.]

1. That must be; that can not be otherwise; indispensably requisite. It is necessary that every effect should have a cause.
2. Indispensable; requisite; essential; that can not be otherwise without preventing the purpose intended. Air is necessary to support animal life; food is necessary to nourish the body; holiness is a necessary qualification for happiness; health is necessary to the enjoyment of pleasure; subjection to law is necessary to the safety of persons and property.
3. Unavoidable; as, a necessary inference or consequence from facts or arguments.
4. Acting from necessity or compulsion; opposed to free. Whether man is a necessary or a free agent is a question much discussed.